Explore Everyday Health

Save

Having Lots of Children May Up Risk of Aggressive Breast Cancer

Women who had three or more children had a higher risk of triple-negative breast cancer, while those who never gave birth had a lower risk of this aggressive form of the disease. On the other-hand, childless women had a greater risk of a more treatable type of breast cancer.

Thanks for signing up! You might also like these other newsletters:

Mon. Feb. 28, 2011 — The risk of triple-negative breast cancer — an aggressive form of the disease — increased by almost 50 percent in women who had given birth three times or more, according to a new analysis data from the Women's Health Initiative.

In contrast, not having any children was associated with a 40 percent lower risk of triple-negative breast cancer — although it did carry a 35 percent greater risk of estrogen receptor-positive cancer.

Researchers haven’t yet looked into biological explanations, but the findings could have implications for more individualized care, according to the study published in the Journal of the National Cancer Institute.

"Given the poor prognosis associated with triple-negative breast cancer, it remains important to identify the factors that influence a woman's risk of developing this subtype of disease and to further characterize if and how such factors differ from risk factors for the more predominant estrogen receptor-positive breast cancer subtype that has a better prognosis," concluded Dr. Amanda Phipps of Fred Hutchinson Cancer Research Center in Seattle, and her co-authors.

Yet few studies have looked at these risk factors in breast cancer overall and particularly in the triple-negative subtype.

The Women’s Health Initiative database afforded an opportunity to perform a more detailed epidemiologic evaluation of hormonal associations with triple-negative breast cancer. Women who participated filled out extensive questionnaires about their reproductive history.

Among 155,723 women, a total of 5,194 developed invasive breast cancer during a median follow-up of about eight years.

The authors could ascertain complete receptor status (estrogen, progesterone, HER2) in 3,116 of the breast cancer patients: 307 with triple-negative disease, 2,610 with ER-positive breast cancer, and 199 who had tumors that were ER negative but positive for other receptors.

Women with triple-negative breast cancer tended to be younger, had larger tumors at diagnosis, were more likely to have a family history of breast cancer, and were more likely to be African American, as compared with women who had ER-positive tumors.

Women with triple-negative and ER-positive breast cancer had distinct reproductive histories. Having no children decreased the risk of triple-negative disease but increased the risk of ER-positive breast cancer.

As well, rates of triple-negative breast cancer were higher in women who’d had kids, while rates of ER-positive cancer were higher in those who’d never given birth.

The risk of triple-negative breast cancer also increased with the number of births. In contrast, the risk of ER-positive breast cancer decreased with an increasing number of births, the researchers said.

Though informative, the results also raised questions.

"It remains unclear why not having children, or having few] would be associated with a decreased risk of triple-negative breast cancer," the authors wrote in the discussion of their study.

"It is also unclear why the difference between ER-positive and triple-negative subtypes would be limited to associations with parity and age at first birth and not extend to differences in associations with other aspects of reproductive history, such as duration of breast feeding, which also influence a woman's cumulative lifetime exposure to endogenous estrogens."